B. Prado

Photocatalytic degradation of trimethoprim by metallic nanoparticles supported on TiO2-P25

The effect of Au, Ag, Cu and Ni nanoparticles deposited on TiO2-P25 was studied on the photodegradation of trimethoprim, a commonly used antibiotic. The synthesized materials were characterized by ICP, EDS, XRD, BET, UV-vis, TEM and TPR. The metal loading was 0.5 wt.% and the average particle size was about 2 nm in all the studied samples. The deposition of metallic particles on TiO2-P25 produces an enhancement of the activity of the bare semiconductor; when the degradation of trimethoprim was carried out by pure TiO2-P25, the mineralization reached only 50% of the organic matter, while by using metallic nanoparticles deposited on TiO2-P25, the mineralization of organic matter increased up to 80% for the same reaction conditions and reaction time. The evaluation of the photocatalytic activity was made for solutions containing trimethoprim in concentrations of 40 ppm under UV light irradiation using a lamp with primary emission at 254 nm and 2.2 mW/cm(2). It is shown that the ability of the photocatalyst to mineralize trimethoprim depends on the electron affinity and the electronegativity of the deposited metal.

Environmental fate of naproxen, carbamazepine and triclosan in wastewater, surface water and wastewater irrigated soil — Results of laboratory scale experiments

Lab-scale photolysis, biodegradation and transport experiments were carried out for naproxen, carbamazepine and triclosan in soil, wastewater and surface water from a region where untreated wastewater is used for agricultural irrigation. Results showed that both photolysis and biodegradation occurred for the three emerging pollutants in the tested matrices as follows: triclosan>naproxen>carbamazepine. The highest photolysis rate for the three pollutants was obtained in experiments using surface water, while biodegradation rates were higher in wastewater and soil than in surface water. Carbamazepine showed to be recalcitrant to biodegradation both in soil and water; although photolysis occurred at a higher level than biodegradation, this compound was poorly degraded by natural processes. Transport experiments showed that naproxen was the most mobile compound through the first 30cm of the soil profile; conversely, the mobility of carbamazepine and triclosan through the soil was delayed. Biodegradation of target pollutants occurred within soil columns during transport experiments. Triclosan was not detected either in leachates or the soil in columns, suggesting its complete biodegradation. Data of these experiments can be used to develop more reliable fate-on-the-field and environmental risk assessment studies.

Impact of long-term wastewater irrigation on sorption and transport of atrazine in Mexican agricultural soils

In the Mezquital Valley, Mexico, crops have been irrigated with untreated municipal wastewater for more than a century. Atrazine has been applied to maize and alfalfa grown in the area for weed control for 15 years. Our objectives were to analyse (i) how wastewater irrigation affects the filtering of atrazine, and (ii) if the length of irrigation has a significant impact. We compared atrazine sorption to Phaeozems that have been irrigated with raw wastewater for 35 (P35) and 85 (P85) years with sorption to a non-irrigated (P0) Phaeozem soil under rainfed agriculture. The use of bromide as an inert water tracer in column experiments and the subsequent analysis of the tracers’ breakthrough curves allowed the calibration of the hydrodynamic parameters of a two-site non equilibrium convection-dispersion model. The quality of the irrigation water significantly altered the soils’ hydrodynamic properties (hydraulic conductivity, dispersivity and the size of pores that are hydraulically active). The impacts on soil chemical properties (total organic carbon content and pH) were not significant, while the sodium adsorption ratio was significantly increased. Sorption and desorption isotherms, determined in batch and column experiments, showed enhanced atrazine sorption and reduced and slower desorption in wastewater-irrigated soils. These effects increased with the length of irrigation. The intensified sorption-desorption hysteresis in wastewater-irrigated soils indicated that the soil organic matter developed in these soils had fewer high-energy, easily accessible sorption sites available, leading to lower and slower atrazine desorption rates. This study leads to the conclusion that wastewater irrigation decreases atrazine mobility in the Mezquital valley Phaeozems by decreasing the hydraulic conductivity and increasing the soils sorption capacity.

Antibiotic pollution in the Katari subcatchment of the Titicaca Lake: Major transformation products and occurrence of resistance genes

An increasing number of studies pointed out the ubiquitous presence of medical residues in surface and ground water as well as in soil compartments. Not only antibiotics can be found in the environment but also their transformation products about which little information is generally available. The development of bacterial resistance to antibiotics is particularly worrying as it can lead to sanitary and health problems. Studies about the dissemination of antibiotics and associated resistances in the Bolivian Altiplano are scarce. We provide baseline information on the occurrence of Sulfamethoxazole (SMX) and Trimethoprim (TMP) antibiotics as well as on the most common human SMX transformation products (TP) and on the occurrence of sulfonamide resistance genes. The studied water and soil compartments presented high levels of antibiotic pollution. This situation was shown to be mainly linked with uncontrolled discharges of treated and untreated wastewaters, resulting on the presence of antibiotics in the Titicaca Lake. SMX TPs were detected in surface waters and on soil sampled next to the wastewater treatment plant (WWTP). SMX resistance genes sulI and sulII were widely detected in the basin hydrological network, even in areas unpolluted with antibiotics. Mechanisms of co-selection of antibiotic- and metal- resistance may be involved in the prevalence of ARGs in pristine areas with no anthropogenic activity and free of antibiotic pollution.

Nitrate Sorption in a Mexican Allophanic Andisol using Intact and Packed Columns

Abstract Contamination of groundwater by nitrate is a worldwide environmental issue. A better knowledge of nitrate sorption characteristics by soils contributes to efficient fertilizer use and prevents aquifer contamination. In volcanic soils, nitrate sorption is induced by variable charges due to the presence of amorphous materials and aluminum (Al) and iron (Fe) oxides. Anion transport in packed and intact columns was investigated in a Mexican Allophanic Andisol, under different permanent flow regimes in unsaturated conditions and several NO3 −‐N and Br− input concentrations. In the packed columns, the NO3 −‐N adsorption in the soil was nonlinear. In the intact columns, the retardation coefficient variation was directly correlated to the increase of amorphous material with depth. The presence of preferential flow in the intact columns significantly increased the mobility and velocity of nitrate moving through the columns, whereas in the packed columns, NO3 −‐N fate was only affected by soil chemical composition and mineralogy.

Fate of atrazine in a soil under different agronomic management practices

Agricultural management affects the movement of atrazine in soil and leaching to groundwater. The objective of this study was to determine atrazine adsorption in a soil after 20 years of atrazine application under agronomic management practices differing in tillage practice (conventional and zero tillage), residue management (with and without residue retention) and crop rotation (wheat-maize rotation and maize monoculture). Atrazine sorption was determined using batch and column experiments. In the batch experiment, the highest distribution coefficient Kd (1.1 L kg−1) at 0–10 cm soil depth was observed under zero tillage, crop rotation and residue retention (conservation agriculture). The key factor in adsorption was soil organic matter content and type. This was confirmed in the column experiment, in which the highest Kd values were observed in treatments with residue retention, under either zero or conventional tillage (0.81 and 0.68 L kg−1, respectively). Under zero tillage, the fact that there was no soil movement helped to increase the Kd. The increased soil organic matter content with conservation agriculture may be more important than preferential flow due to higher pore connectivity in the same system. The soils capacity to adsorb 2-hydroxyatrazine (HA), an important atrazine metabolite, was more important than its capacity to adsorb atrazine, and was similar under all four management practices (Kd ranged from 30 to 40 L kg−1). The HA adsorption was attributed to the type and amount of clay in the soil, which is unaffected by agronomic management. Soils under conservation agriculture had higher atrazine retention potential than soils under conventional tillage, the system that predominates in the study area.

NIR spectroscopy to identify and quantify imazapyr in soil

The analysis of herbicide residues applied to the soil is commonly conducted by using chromatographic techniques which use organic solvents, are costly and time consuming. Having a simple and inexpensive discriminant method to determine samples with and without herbicide residues would be highly beneficial to lower costs of analysis and save time. The general objective of the present work was to develop such methodology. In particular, the presence of imazapyr was quantified using a near-infrared spectroscopy (NIRS) and a chemometrics approach. The experimental soil for a qualitative experiment of discrimination was Phaeozem with different agricultural managements and the following treatments: dry soil doped with imazapyr, rehydrated soil also doped with the herbicide, and control soil without the chemical. A discriminant algorithm was developed to allow the identification of soils containing imazapyr and those which did not contain the herbicide. The qualitative approach was based on a discriminant partial least squares (DPLS). An accurate identification of 100 percent of the soils containing imazapyr and 98 percent of those which did not contain the pesticide was achieved. Quantification of imazapyr was performed in five soil types (Andosol, Vertisol, Acrisol, Cambisol and Phaeozem) with different concentrations of the herbicide with an equation generated by modified partial least squares (MPLS) regression. As a reference for the above analytical method, a high performance liquid chromatography (HPLC) analysis was performed. The resulting equation had a RSQ of 0.81 and a prediction capacity (RPD) of 2.4. The results showed that with NIR spectroscopy it was possible to discriminate soils that contained imazapyr from those that did not contain the herbicide. This finding allows for a reduction in the number of samples to be evaluated to determine their concentration. Moreover, with this technique it is also possible to estimate the amount of herbicide in the soil with similar results to those accomplished using the reference method (HPLC), but faster and at lower cost.

Quantifying preferential flows in porous soils: An original imaging and image processing procedure

With the increasing accessibility of image acquisition techniques, image processing has become an essential component of soil science. Here, Image Processing is specifically used to the accurate prediction of solute transport through soils. To do so, dye tracers are leeched into soil cores to visualize active flow paths in cross sections of soil. We have derived a cheap alternative, using off-the-shelf equipments, as compared to earlier experiments. We still managed to compensate for most of the images acquisition process noise and provided a simple yet correctly correlated data analysis and dye concentration estimation. We tested the method using a fluorescent dye (pyranine) in intact soil cores of a Mexican allophonic (volcanic) soil. The current application of this procedure is the estimation of the pharmaceutical compounds (mostly antibiotics) contamination of agricultural soils irrigated by waste water in the northern central region surrounding Mexico City.

Visualising 3D porous media fluid interaction using X-ray CT data and Smooth Particles Hydrodynamics modelling

We propose the use of the Lagrangian method Smoothed particle Hydrodynamics (SPH) to model the behaviour of fluids through a pore structure of a volcanic soil core sample. Such studies are of importance to simulate preferential flows which are essential in the leeching of organic and chemical compounds in underground aquifers. Our approach combines X-ray Computed Tomography imaging, and image processing techniques to extract the 3D porous structure of the media studied. Smoothed particle Hydrodynamics modelling simulates water transport in the reconstructed 3D pore network using Navier Stokes governing laws. An isolated pore was considered as a case-based study. We are currently extending our simulation to a full sized pore network.